In retail distribution centers, boxes of goods are transported on a moving conveyor for routing to various locations in the center. It is desired to sequence the order of the boxes traveling on the conveyor. Known approaches include positioning optically readable patterns on the boxes and optically reading the boxes as they pass an imager. Such imagers represent a significant expense to the distributor. Other approaches involve the use of radio frequency identification (RFID) tags on the boxes which are read by RFID tag readers. However, the principle challenge for using RFID technology on a conveyor is identifying the sequence order of the boxes on the conveyor. The boxes on a conveyor are filled with various types of content. One box may have tissue paper and another one shampoo. The tag attached to the tissue paper box will respond to an RFID reader at greater distances than the tag attached to the box of shampoo. The consequence of this is that the tag on the tissue box will likely read before the tag on the shampoo box. The reader will think that the tissue box is in front of the shampoo box even though it is actually behind. All efforts to solve this with phase shift, RSSI, and the like calculations have failed to provide an accurate and reliable sequencing capability. The principle problem with these solutions is that they struggle with the unpredictability of the path that RF energy follows when it is reflected off the surfaces of the structures in the facility.
Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. Certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. The terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein.